The present invention relates to a deflection yoke and a cathode-ray tube device for use as a computer display unit, for example.
Heretofore, efforts have been made to reduce image distortions and misconvergence in cathode-ray tube devices for use as computer display units or the like by adjusting the winding distribution of deflection coils and correcting deflecting magnetic fields with an auxiliary coil.
Specifically, it is possible to reduce image distortions and misconvergence in a cathode-ray tube device simply by adjusting the field distributions of deflecting magnetic fields in order to produce different field distributions of horizontal and vertical deflecting magnetic fields at screen and neck regions of the cathode-ray tube device (see Japanese Patent Laid-open Nos. Hei 4-65489, Hei 4-39649, and Hei 5-39895).
If the field distributions of horizontal and vertical deflecting magnetic fields differ from each other at screen and neck regions of a cathode-ray tube device, however, a reversed pattern of misconvergence is produced on the display screen as shown in FIG. 1 of the accompanying drawings. In FIG. 1, "XH" represents an amount of misconvergence produced on a central line in left and right end areas of the display screen, "XH'" represents an amount of misconvergence produced in areas between the left and right end areas and the center of the display screen, and "S1", PQV represent amounts of misconvergence produced in upper and lower areas above and below the areas where the amounts of misconvergence "XH", "XH'" are measured.
In the upper and lower areas, red and blue patterns are vertically reversed as they go from the center of the display screen toward the left and right end areas thereof. Because of the reversed red and blue patterns, if misconvergence is reduced in some area of the display screen by changing the deflecting magnetic fields, then misconvergence is increased in another area of the display screen. For correcting the misconvergence by changing the deflecting magnetic fields, however, it is difficult to set the winding distributions of deflection coils to optimum values and also to adjust the deflection yoke.
To alleviate such a drawback, it has been customary for related art cathode-ray tube devices to incorporate an auxiliary coil in the deflection yoke near the electron guns. The auxiliary coil is energized by a horizontal deflecting current or a current from an external power supply. Alternatively, the auxiliary coil consists of a saturable reactor, and is modulated by a vertical deflecting current and energized by a horizontal deflecting current. The auxiliary coil is thus energized to correct the misconvergence which cannot fully be removed by the deflection yoke itself (see Japanese Patent Laid-open Nos. Sho 60-158534, Hei 5-1890, and Hei 5-15715).
However, use of the auxiliary coil separately mounted on the neck of the cathode-ray tube for convergence correction results in an increased number of parts of the cathode-ray tube device, which is therefore relatively complex in structure.